The present disclosure relates to lubrication systems for gas turbine engines and more particularly to a solution for overcoming oil coking in the lubrication system.
Every gas turbine engine includes bearings to support the rotary shafts of the engine. The bearings are typically housed in bearing compartments that are connected to a lubrication system. The lubrication system provides lubricant, such as oil, to the bearing compartment through a supply line to lubricate and cool the bearings. The lubrication system also recovers the oil from the bearing compartment through a scavenge line and sends the oil through a filter and heat exchanger before cycling the oil back to the bearing compartment.
At shutdown of the gas turbine engine, the lubrication system ceases to circulate oil to the bearing compartment and the oil, now without pumping pressure, drains out of both the supply line and the scavenge line and back to a sump or nose point in the lubrication system. With the lubrication system inactive and no longer dissipating heat from the bearing compartment, heat produced by the gas turbine engine just prior to shutdown can “soak back” into both the bearing compartment and the supply and scavenge lines and can excessively elevate the temperature of these engine components. The elevated temperatures caused by the heat soak back can cause oil mist or oil film located in the supply line and the scavenge line to react with air and form coke deposits on the inside surfaces of the supply line and the scavenge line. Over time, these coke deposits can accumulate and clog the supply line and the scavenge line and starve the bearing compartment of oil. Without an adequate supply of oil, the bearings in the bearing compartment can fail and result in engine-wide failure of the gas turbine engine.